Polymers of unsaturated hydrocarbons stabilized with ruthenium tetroxide

ABSTRACT

THE ULTRAVIOLET LIGHT STABILITY OF POLYMERS OF UNSATURATED HYDROCARBONS IS IMPROVED BY IMMERSING THE POLYMERS IN A SOLUTION OF RUTHENIUM TETROXIDE IN CARBON TETRACHLORIDE. AFTER EXPOSURE TO ULTRAVIOLET LIGHT, THE POLYMERS SO TREATED RETAIN THEIR MECHANICAL PROPERTIES TO A SUBSTANTIAL EGREE, AND CRAZING OR CRACKING OF THE POLYMERS IS VIRTUALLY ELIMINATED.

United States Patent O 3,838,090 POLYMERS F UNSATURATED HYDROCARBONS STABILIZED WITH RUTHENIUM TETROXIDE Richard J. Dauksys, Bellbrook, Ohio (49 Nuthatch Knob Road, Glastonbury, Conn. 06033) No Drawing. Filed Apr. 2, 1973, Ser. No. 347,242

Int. Cl. (308E 45/56, 45/62; C08g 45/56 US. Cl. 26045.75 R 3 Claims ABSTRACT OF THE DISCLOSURE FIELD OF THE INVENTION This invention relates to a process for stabilizing polymers of unsaturated hydrocarbons against degradation by ultraviolet radiation. In one aspect it relates to stabilized polymers of unsaturated hydrocarbons, particularly homopolymers and copolymers of ethylene and propylene.

BACKGROUND OF THE INVENTION Polymers of unsaturated hydrocarbons, such as ethylene and propylene, are susceptible to degradation when exposed to light. The degradation is especially severe when the polymers are subjected to exposure to light in the ultraviolet portion of the spectrum. The degradation that occurs generally results in the loss of tensile strength and other physical properties and in cracking or crazing caused by embrittlement. A variety of materials, e.g., titanium dioxide, carbon black, and mixtures of dithiocarbamates, are disclosed in the prior art as being suitable for stabilizing polyethylene or polypropylene against degradation by ultraviolet light. When utilizing such stabilizing ingredients, they are usually admixed with the melted polymer, for example, by milling on heated rolls or by employing a Banbury mixer. This procedure is carried out prior to the fabrication of the desired article by molding, extrusion or other suitable method.

It is an object of this invention to provide a new and simplified procedure for stabilizing polymers against degradation by ultraviolet light.

Another object of the invention is to provide a process for stabilizing polymers that does not require the mixing step of the prior art processes whereby stabilizing agents are incorporated into the polymers.

A further object of the invention is to provide a process whereby articles fabricated from hydrocarbon polymers can be stabilized subsequent to their fabrication.

Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.

SUMMARY OF THE INVENTION Broadly speaking, the present invention resides in a process for stabilizing a solid hydrocarbon polymer against degradation by ultraviolet light whereby the polymer is immersed in a bath comprising a solution of ruthenium tetroxide in carbon tetrachloride. It has been discovered that treatment of the polymer in this manner results in a product which retains its physical properties to a substantial degree and is not subject to cracking after exposure to ultraviolet light. The mechanism whereby the polymer is stabilized is not completely understood. While it is not intended to limit the invention to any particular theory, it is believed that the ruthenium tetroxide permeates the polymer by diffusion, causing cleavage of terminal carbon to carbon double bonds, which are susceptible to ultraviolet light. Thus, ruthenate ester groups are formed that are much less subject to ultraviolet light degradation.

The process of this invention is, in general, applicable to the stabilization of polymers of unsaturated hydrocarbons against degradation caused by exposure to ultraviolet light. Examples of such polymers include polymers of aolefins, preferably containing 2 to 4, inclusive, carbon atoms, and of conjugated dienes, preferably containing 4 to 6, inclusive, carbon atoms. Homopolymers as well as copolymers of a-olefins and conjugated dienes can be treated in accordance with the process of this invention. Exemplary of such polymers are polyethylenes, polypropylenes, polyisobutylenes, ethylene-propylene copolymers, polybutadienes, polyisoprenes, butadiene-styrene copolymers, and the like. Such polymers are well known, and various methods for their preparation are described in the literature.

In carrying out the process of this invention, the ruthenium tetroxide is dissolved in carbon tetrachloride. The amount of ruthenium tetroxide added to the solvent is usually in the range of about 0.05 to 2.0 grams per liter of solution. The polymer to be stabilized is immersed in the solution for a period of about 5 minutes to 5 hours, preferably from about 0.5 to 1.5 hours. During the period of immersion, the solution is maintained at a temperature in the range of about 20 to 76 C.

The process of this invention is particularly applicable to stabilizing articles fabricated from hydrocarbon polymers. Such articles include polymeric sheets or film, castings, compression or injection molded items, and extruded items such as fibers and rod stock.

A more complete understanding of the invention can be obtained by referring to the following illustrative example which is not intended, however, to be unduly limitative of the invention.

EXAMPLE A series of runs was conducted in which polyethylene and polypropylene were stabilized against degradation by ultraviolet light in accordance with the process of this invention. The solution used in the runs consisted of 1 gram of ruthenium tetroxide dissolved in 420 milliliters of carbon tetrachloride. Specimens of polyethylene and polypropylene were immersed in the solution maintained at a temperature of 23 C. The specimens were dogbone tensile specimens which had been stamped from sheets of polyethylene and polypropylene using a metal die.

At the end of the immersion time, the specimens were dried and then exposed to ultraviolet light for a period of 200 hours. The ultraviolet light exposure was conducted in an Atlas Weather Ometer (Model XW). Distance of the specimens from the ultraviolet source generated by carbon electrodes was 14 inches.

Control runs were also carried out in which untreated specimens were exposed to ultraviolet light in the manner described in the preceding paragraph.

The tensile strength of the treated and untreated specimens was determined, using an Instron Universal Testing Machine. Specimen width in the gage section was 0.25 inch and the gage length was 1 inch. The method of ASTM D638-60T was used as a guide in the testing procedure.

The results of the tests as well as information concerning conditions of the runs are shown hereinafter in the table.

TABLE Percent'retention tensile load Age of Condition of Immersion Solution solution, Polyeth- Polyprospecimen 1 time, hrs. temp., hr. yleno pylene A 75 60 B 1 23 315 92 83 B 2 23 337 90 77 1 Control runs.

From the data in the foregoing table, it is seen that the untreated specimens of polyethylene and polypropylene lost from about 25 to 30 percent of their original tensile strength when exposed to ultraviolet light for 200 hours. On the other hand, the polyethylene specimens that were treated in accordance with the process of this invention underwent a loss in tensile strength of only 8 to 10 percent. While the tensile strength retention was not as great for polypropylene, there was a substantial improvement as compared to the untreated specimens. The treated specimens did not exhibit any sign of crazing as did the untreated specimens.

As will be evident to those skilled in the art, various modifications of the invention can be made or followed in view of the foregoing disclosure without departing from the spirit or scope of the invention.

I claim:

1. A stabilized polymer composition comprising a polymer of an unsaturated hydrocarbon stabilized against degradation by ultraviolet light by the method of afiecting stabilization which comprises immersing the article in a solution of ruthenium tetroxide in carbon tetrachloride, the solution being at a temperature ranging from about 20 to 76 C., and the solution containing about 0.05 to 2.0

References Cited UNITED STATES PATENTS 3,111,533 11/1963 Ecke 26045.75 3,117,148 1/1964 Ihrman et a1. 26045.75 3,313,835 4/1967 Wilkus et al. 260-45.75 3,309,219 3/ 1967 Etherington 252300 2,972,604 2/1961 Reynolds et al. 26033.6 2,049,488 8/1936 Braun 423592 OTHER REFERENCES Plastics & Polymers, June 1968, pp. to 203.

V. P. HOKE, Primary Examiner UNIT D STATES PATENT OFFICE CERTIFICATE CORRECTION Patent No. 3,838,090 Dated September 24, 1974 I nrentor(s) Richard J. Dauksys c It is certified that error appears in the above i der ztified' patent and that'said Letters Patent are hereby corrected as shown below:

Column 4, line 13, change "or" to to I,

sighed-"aid seeled this 17th day ofDecefiiber 1974.

MR v v, V McCOY M. cIBso' /JR.' 4 I I c. MARSHAL -DAMN I Att-e'sting Officer ComissionerflqflPatents 

